Methods for detecting an x-ray include a method of directly detecting an x-ray and a method of indirectly detecting an x-ray by converting the x-ray into a visible ray and then detecting the x-ray using the visible ray.
An x-ray detector using the aforementioned indirect method includes an element to convert an x-ray into a visible ray, an element to convert the visible ray into an electronic signal, and an element to convert the electronic signal into an image signal. In other words, the x-ray detector using the indirect method is an apparatus configured to convert an emitted x-ray eventually into an image signal.
A conventional digital x-ray detector (hereinafter referred to as a ‘digital x-ray detector’) will be explained with reference to the drawings attached.
FIG. 1 is a schematic cross-sectional view illustrating a conventional digital x-ray detector and FIG. 2 is a schematic top view of the conventional digital x-ray detector. As illustrated in FIGS. 1 and 2, the conventional digital x-ray includes a substrate 10, a gate line 20 and a data line 30 disposed on the substrate 10 such that the gate line and the data line 30 intersect each other, a thin film transistor 40 formed on an intersecting region of the gate line 20 and the data line 30, a PIN diode 50 disposed on a pixel domain, a bias line 60 disposed above the PIN diode 50 such that it is parallel to the data line 30, and a scintillator 70.
The thin film transistor 40 is formed on the substrate 10, and includes a gate electrode 21, an active layer 41, a source electrode 42, and a drain electrode 43.
The PIN diode 50 includes a lower electrode 51 that is electrically connected to the thin film transistor 20, a PIN layer 52 that includes a P (Positive) type semiconductor layer, an I (Intrinsic) type semiconductor layer, and an N (Negative) type semiconductor layer successively deposited on the lower electrode 51, and an upper electrode 53 made of a transparent conductor such as ITO (Indium Tin Oxide).
The scintillator 70 is formed on the PIN diode 50 and serves to convert an x-ray into a visible ray.
Hereinafter, operations of such a conventional digital x-ray will be explained.
When an x-ray is emitted to the scintillator 70, the x-ray is converted into a visible ray in the scintillator 70, and then the visible ray is transmitted to the PIN diode 50. The visible ray transmitted to the PIN diode 50 is converted into an electronic signal in the PIN diode 50, and the converted electronic signal is converted into an image signal through the thin film transistor, and is then displayed.
A reaction velocity of the digital x-ray detector is determined by a capacitance of the PIN diode 50. Specifically, an area of the upper electrode 53 that forms the PIN diode 50 is closely related to the capacitance of the PIN diode 50. That is, the capacitance (C) of the PIN diode 50 is proportional to a dielectric constant (∈) of the dielectric and an area (A) of the lower electrode 51 and the upper electrode 53 and is inversely proportional to a distance (l) between the lower electrode 51 and the upper electrode 53.
However, a conventional PIN diode 50 is formed such that it fills most of a pixel domain defined by the gate line 20 and the data line 30. Therefore, as the area of the upper electrode 53 increases, the capacitance of the PIN diode 50 increases, and such increased capacitance becomes a reason for deteriorating the reaction velocity of the digital x-ray detector.
Furthermore, the visible ray being provided from the scintillator 70 towards the PIN diode 50 is partially absorbed or reflected according to material characteristics of the upper electrode 53 and, thus, does not reach the PIN layer 52 below the upper electrode 53, that is, there is a problem that the upper electrode 53 deteriorates photo-electron signal conversion efficiency of the PIN diode 50.
Thus, a need exists to overcome the problems with the prior art systems, designs, and processes as discussed above.